The present invention relates to a fuel injection system of an internal combustion engine having at least one cylinder cooperating with a piston activated to rotate a drive shaft. More specifically, the invention relates to an injection system comprising a pump having at least one pumping element activated to pump high-pressure fuel; a rail for the fuel so pumped; and an injector for injecting a given quantity of fuel from the rail into the engine cylinder.
In old diesel engines, the injectors are supplied directly by a high-pressure fuel pump, the delivery of which is temporarily discontinuous, timed with the engine, and cyclically constant, i.e. a pump activated in synchronism with the injectors. This type of operation poses problems in adapting delivery of the pump to draw by the injectors, in the event of sharp variations in engine speed or load.
In modern internal combustion injection engines, each injector draws high-pressure fuel from a so-called xe2x80x9ccommon railxe2x80x9d, which forms a fuel reserve for the injectors and is normally supplied by a high-pressure piston pump in turn supplied with fuel from the fuel tank by a low-pressure pump.
In modern engines, the high-pressure pump of known injection systems has a temporarily continuous delivery not timed with the engine, i.e. is activated, for example, by a cam and therefore supplies fuel substantially continuously to the common rail, whereas the injectors are activated at a predetermined stage in the engine cylinder cycle. The fuel pressure in the common rail is controlled by a pressure regulator, but, to cater to large withdrawals of fuel, the common rail must be of considerable volume and, therefore, size. The pump must also be sized to cater to maximum fuel withdrawal by the injectors as a whole during the engine cycle, so that the volumetric efficiency of the pump is relatively poor.
Known common-rail injection systems therefore cannot be fitted to old engines with injectors supplied directly by the high-pressure pump, on account of the bulk of the injection system, and the temporarily discontinuous delivery of the high-pressure pump, which is therefore unsuitable for common-rail injection systems.
Moreover, the pressure regulator of known common-rail injection systems normally comprises a valve controlled by an electromagnet and located between the high-pressure pump and the common rail. When the valve is closed, the fuel pumped by the high-pressure pump is fed to the rail; and, when the valve is opened partly or fully, the surplus fuel pumped is drained along a drain conduit back into the tank.
In known technology, the pressure regulating valve is closed by the electromagnet when this is energized, and is kept open by a spring when the electromagnet is deenergized, so that the electromagnet is energized by a high current to open the valve partly to regulate the fuel pressure. Moreover, if the electromagnet fails to be energized during operation of the engine, the valve is opened fully by the spring, thus draining the common rail completely and arresting the engine.
It is an object of the present invention to provide an internal combustion engine fuel injection system, which provides for a high degree of reliability, is cheap to produce, and eliminates the aforementioned drawbacks typically associated with known injection systems.
According to the present invention, there is provided a fuel injection system for an internal combustion engine having at least one cylinder cooperating with a piston activated to rotate a drive shaft; said system comprising a pump having at least one pumping element activated intermittently to pump high-pressure fuel; a fuel rail communicating with a delivery conduit of said pump and for receiving the fuel so pumped; and at least one fuel injector communicating with said rail and activated to draw a given quantity of fuel from said rail and inject it into said cylinder; and said quantity varying according to the instantaneous load of said engine; characterized in that said pumping element has a delivery at least equal to the maximum draw of said injector; and said pumping element being activated in pumping phase with said injector to minimize the variations in fuel pressure in said rail.
More specifically, in the case of an internal combustion engine having a number of cylinders associated with a corresponding number of injectors communicating with the rail, the pumping element has a delivery at least equal to the maximum draw of each of said injectors, and is activated in pumping phase with a corresponding injector in said number.